Ink jet inks are well known in the art and are typically liquid compositions comprising a carrier liquid, colorants such as dyes or pigments, and optional additives such as thickeners and preservatives to obtain the desired properties. Different types of colorants may be used for inks, for example, simple color pigments and water-soluble dyes.
Novel pigments have been found which resemble naturally occurring opals and wherein the color activity is produced by Bragg diffraction of the incident light on the grid planes of the spheres arranged in a crystal-like manner on the substrate surface (the spheres diffract the light according to Bragg's law).
WO01/88044 describes pigments with an opalescent effect. The pigment particles consist of monodisperse spheres in a three-dimensional, tightly packed and regularly arranged structure, also called three-dimensional photonic crystals, with a diameter of 50 nm to 2 μm. The pigments may be prepared by suspensing of the monodisperse spheres in a liquid medium, applying the suspension on a surface, removing the liquid medium and separating the particles from the surface. The pigments may be used for coating substrate surfaces and the pigmentation of printing paints, e.g. in the way of pigment pastes, in combination with inorganic or organic colorants.
According to WO03/058299 such particles are fixed in a polymeric matrix for the use as pigment particles in coating compositions.
EP-A-0955323 describes core/shell particles that may be used as special effect pigments for the use in coatings, paints and inks. With respect to their cores, the particles may have a regular arrangement and are based substantially on high molecular polymers. The particulated pigments may be applied to the substrates in the form of solid, liquid or paste preparations with the aid of auxiliary constituents and additives.
In EP-A-1184195, an ink jet method is described wherein the ink jet recording material such as paper or plastic comprises a top layer containing core-shell particles of refractive nature.
The disclosures of all of the above-identified publications are incorporated by reference herein for all purposes as if fully set forth.